The invention relates to a light analyzer as a double beam type spectrophotometer having two-systematic optical paths, such as a sample side beam and a reference side beam. The light analyzer includes an optical path structure for introducing a measuring light including plural states into a light-sensitive detector by subjecting the measuring light to time-division multiplexing or intensity modulation.
For example, in a double beam-type ultraviolet visible light spectrophotometer, light irradiated from a light source is introduced into a spectroscope to take out a monochromatic light having a specific wavelength, and the monochromatic light is alternately distributed as a sample side beam and a reference side beam by a rotation sector mirror or the like. After the respective beams have passed through a sample cell and a reference cell, they enter a single light-sensitive detector, so that photoelectric transfer is made to take out electric signals. The rotation sector mirror is provided with a portion, which intercepts light as the mirror is rotated, and an output of the light-sensitive detector corresponding to the portion becomes a zero signal z, so that a ratio (s-z)/(r-z) of an electric signal r with respect to a light quantity of the reference side beam and an electric signal s with respect to a light quantity of the sample side beam becomes a measured result. Or, with the interception of the light, a zero signal zs corresponding to the sample side beam and a zero signal zr corresponding to the reference side beam can be obtained, respectively, and (s-zs)/(r-zr) may be the measured result.
More specifically, in the device having the above structure, the output of the light-sensitive detector is in a time-divisional-multiplexed state of the signal r, signal s and zero signal z (or zs and zr). Also, in view of the input of the light-sensitive detector, it can be assumed that the sample side beam containing information relative to the sample cell, the reference side beam containing information relative to the reference cell and the cutoff period are applied, i.e. time-divisionally-multiplexed. In the conventional device, after the time-divisionally-multiplexed light signals thus received are separated by an analog switch, i.e. demultiplexer, respectively, they are inputted into an analog-digital converter (hereinafter referred to as xe2x80x9cA/D converterxe2x80x9d), separately, to convert into digital values. Also, there has been known a structure that, instead of the A/D converter, a voltage-frequency converter (hereinafter referred to as xe2x80x9cV/F converterxe2x80x9d) is used, and output signals of the V/F converter are counted for a predetermined period to thereby obtain the digital values.
In the above structure, it is unavoidable that the output signals are changed when the signals are selectively switched by the analog switch. Therefore, when the digital values are subjected to the data processing, for example, there is required a troublesome process such that the samples immediately before and after changing the analog switch must be removed. Also, a signal for determining the switch timing of the analog switch is required to be produced in synchronization with the rotation of the sector mirror. Therefore, while a position detecting mechanism attached to the sector mirror or a motor for rotating the sector mirror is used, due to an error of the attaching position, accuracy of the signal switching is low.
Further, for example, since a dynamic range in the order of 20 bits is required in a self-registering spectrophotometer, the converting bit number of the A/D converter is necessary to be higher than 20 bits. While the high performance A/D converter as described above is generally expensive, the above-described conventional structure requires a plurality of the A/D converters, and this results in a high cost. Also, in case the plural A/D converters do not have the uniform characteristics, a measuring error occurs. Thus, a selection of the A/D converter is limited.
Incidentally, in addition to the double-beam-type spectrophotometer as described above, for example, in a light-sensitive analyzer having an optical path structure wherein the light is turned on or off, i.e. when widely speaking, intensity is modulated, by allowing beam to periodically intercept by using, for example, a chopper, there is also the same problem.
In view of the above defects, the present invention has been made, and an object of the invention is to provide a light-analyzer having an optical path structure, wherein measuring light is time-divisionally-multiplexed or modulated, and a signal process portion can be structured by a single A/D converter without using an analog switch.
Another object of the invention is to provide a light-analyzer as stated above, wherein the time-divisionally-multiplexed light signals can be, accurately and entirely, separated without influence of the attaching position of a position detecting mechanism for detecting a rotation position of a sector mirror or a chopper.
Further objects and advantages of the invention will be apparent from the following description of the invention.
In order to attain the above objects, according to the invention, there is provided a light-analyzer having an optical path structure wherein a plurality of beams and/or cutoff periods are periodically obtained, i.e. time-divisionally-multiplexed, and introduced into a single light detector. The light-analyzer includes: a converting device for sampling outputs detected by the light-sensitive detector at a predetermined time interval and converting the sampled outputs to digital data; a reference signal generating device for generating a signal in synchronization with a period of the sampled outputs, i.e. the time-division-multiplexing; a memory device for storing the digital data; a data write controlling device for generating an address corresponding to a cycle of the time-division-multiplexing or at least allowing the cycle to be identified by using the reference signal, and sequentially storing the digital data into the memory device; and a data separating device for separating the digital data corresponding to the plural beams and/or cutoff periods by using the address or further determining the read-out digital data values when the digital data stored in the memory device are read out.
The xe2x80x9cplural beamsxe2x80x9d mentioned herein means, for example, the sample side beam and the reference side beam in the double-beam-type device.
Also, a specific example of the xe2x80x9cplural beams and/or cutoff periods are periodically time-divisionally-multiplexedxe2x80x9d is considered such a case that, for example, two beams are alternately selected, or a part or parts of one beam or two beams are cutoff, by a rotation sector mirror or a chopper. In this case, the reference signal generating device generates a signal in synchronization with the rotating period of the sector mirror or the chopper.